Audacity is a free multi-track wave (audio) editor.
Features:
Full record and edit functionality.
Import and export WAV, AIFF, Ogg Vorbis, MP3 and more.
Unlimited Undo.
Amplitude envelope editor.
Customizable spectrogram mode.
Frequency analysis window.
Many built-in effects.
Macros and Scripting options.
Supports VST, AU and LV2 plug-ins.